This invention is directed to a linear energy management unit or cush. More particularly, the present invention is directed to an energy management unit having a long stroke. This cush is an improvement over that which is described and claimed in U.S. Pat. No. 5,511,759 entitled xe2x80x9cHydraulic Chair Height Adjustment Mechanismxe2x80x9d in which the assignee of the present invention has an interest, which is hereby incorporated by reference.
In the above cited patent, a closed-cell microcellular urethane foam member which is coated with a fluid-impervious urethane material is placed in the fluid compartment of a seat height adjustment device. An elastomeric bladder is used to store energy and to raise the seat to a fully extended position from which adjustment can be made. The hydraulic fluid used in the adjustment mechanism is incompressible and would provide anyone sitting in the chair a jolt or shock. The purpose of the cush is to provide a softer feel, to effectively cushion the system such that when a person is first seated in the chair, the incompressible fluid can compress something other than his or her backside.
There are several problems with this type of cush. Firstly, it is limited in its ability to effectively cushion a load, i.e., it has a short stroke. Secondly, there is no possibility to preload the cush. This is important as adjustable height chairs are brought into regulatory compliance. Current test standards require that the chair be able to have adjustability over a given stroke length when loaded with a weight of 130 lbs. Without the benefit of a preload, the seat will sag under load and additional stroke length will need to be afforded resulting in added component length and added expense. Thirdly, repeated cycling in the fluid environment results in some of the cells of the cush collapsing further reducing the cushioning effectiveness of the device.
In order to make the energy management unit more effective, as well as more versatile, i.e., capable of use in other applications, a significant re-thinking of the cush was necessary. The preferred embodiments of the present design provide an energy management unit that is a self-contained capsule which can simply be inserted into the system with which it is used. The elastomeric portions of the cush are isolated from the hydraulic fluid of the host system so that costly coatings can be avoided. Further, the present cush design is a linear device with an extended stroke to provide significantly greater cushioning than was previously possible.
A relatively unstable, collapsible elastomeric member is provided with guide means throughout its length (either circumferential or longitudinal). This elastomeric member is confined within a cylindrical sleeve to stabilize its movement. One end of the sleeve is plugged and the other end is provided with a slidable piston. The elastomeric member may be precompressed a desired amount (for the seat height adjuster application, by an amount sufficient to offset the 130 lb. weight). A protruding piston head can be provided with an O-ring to provide a sealing engagement with an inner cylinder which houses the capsulized cush to isolate the elastomeric member from the working fluid. The guide means engages the internal surface of the guide tube and provides damping of movement between the piston and the guide tube. A second embodiment for non-fluid applications is also provided. Adjustment capability for the precompression of the elastomeric means can be provided for appropriate applications.
Other features, advantages and characteristics of the present invention will become apparent after a reading of the following detailed description of the preferred embodiments.